Abstract: The association of infectious mononucleosis and an immunocompromised host such as occurs in acute leukemia is reported. The most common cause of infectious mononucleosis is Epstein–Barr virus (EBV) and cytomegalovirus (CMV). Patients with mononucleosis syndrome caused by other agents are rare. We report a case of acute monocytic leukemia (AMoL) who developed varicella zoster virus (VZV) mononucleosis syndrome in the bone marrow recovery phase after myelosuppression due to high-dose cytarabine. Mononuclear leukocytes appearing during the mononucleosis syndrome were very similar to the initial leukemic cells. Varicella zoster virus mononucleosis syndrome was confirmed by delayed herpes zoster rash with dermatomal distribution.